Discovered during the Shades of Mort'ton quest, Serum 207 is a temporary cure to the afflicted villagers of Mort'ton, who are otherwise incoherent. It is made through the Herblore skill and requires a minimum level of 15. Its ingredients are Tarromin and Ashes, and gives 50 experience when made. Although it is a good way to use up Tarromin for Herblore experience, the potion's main practical use is during and after the Shades of Mort'ton quest. Most herbalists will make and empty Serum 207, though it can be used on Mort'ton residents for an inexpensive, if slow, method of training Herblore, as the residents will reward the player with ingredients for more serum. If Serum 207 is used on the sacred flame at the rebuilt temple in Mort'ton, it will become Serum 208. For more on that process, see Shades of Mort'ton (minigame). Serum 208 can be used on afflicted residents for a greater reward than the player receives after using Serum 207. This includes ingredients for Serum 207, as well as Bronze keys and Level 1 clue scrolls.

This item can't be withdrawn as a note, so players should keep this in mind before making large quantities of serum.

This potion is different to many other potions, as the secondary ingredient can be placed into the vial before the herb, to make an Ash potion(unf), as well as the standard way around where the herb is added first.